i mean is it possible to dump lanman hashes from users from a other pc in the same domain...

only if you're logged on to the domain server itself ...
use pwdump4 for it than

Alexander01 did you try with lc5 with the sniffing option ?

yes but when does it sniff something?... i think if someone logs in?

Try sniffing at night

First, use Cain&Abel to sniff NTLM from LAN, it's quite easy, and MUCH more efficient than LC5 for that task

Then, use to internal Cain cracker (rainbow tables, bruteforce, dic) or export the hash in .lc format so as to use LC to crack it.

Enjoy LAN hacking